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GROUND WATER SYSTEM <br />A detailed discussion of ground water hydrology is presented under Rule 2.04.7(1). The proposed life -o# -mine <br />area for the Foidel Creek Mine is located within the Twentymile Park ground water basin. The Twentymile <br />Park Basin is an enclosed ground water basin, therefore, any mining- related impacts on the ground water <br />hydrologic system should be confined within the basin. <br />Potential Mining, - Related Impacts on Ground Water Quantity and Quality <br />The mining and related operations have the potential to locally affect the water levels, and the water chemistry <br />of the ground water contained in the Twentymile Sandstone aquifer, the Wadge and Wolf Creek coal and <br />overburden units, and the Trout Creek Sandstone aquifer. The Wadge and Wolf Creek coal and overburden <br />units will be directly affected due to removal of the Wadge and Wolf Creek coal seams. The Twentymile <br />Sandstone and the Trout Creek Sandstone aquifers may be affected if significant hydrologic communication is <br />established with the underground workings. This is not likely to occur except in the vicinity of major fault <br />zones or if greater than predicted subsidence results, due to the existence of thick, intervening bedrock <br />sequences of very low permeability as described in the general description of geology and hydrology (Sections <br />2.04.5, 2.04.6 and 2.04.7). Mining to date has resulted in no significant hydrologic communications between the <br />active or scaled mine workings and these two aquifers. <br />During the mining operation, the major ground water effects will be on water quantities in the immediate <br />overburden. Ground water inflows from the overburden into the mine workings may result in localized, <br />temporary dewatering of portions of the overburden sequence overlying the mine workings and cause drawdown <br />of potentiometric levels at some distance from the mine. If significant hydrologic communication is established <br />with the Twentymile Sandstone or the Trout Creek Sandstone, then drawdown of potentiometric levels in these <br />units may also occur. Discharge of these bedrock aquifers to surface streams may be reduced as a result of these <br />drawdowns. The extent of these effects is examined in more detail under Rule 2.05.6(3)(b)(iii), Probable <br />Hydrologic Consequences, of this revision application. <br />No water quality effects in these units are anticipated during the mining operation, as flows will be from the <br />units to the workings. Mine inflows will be collected in sump areas within the mine and pumped to the surface <br />where they will be treated and either recycled or discharged to surface streams. The effects of this operation on <br />surface water flows and quality are discussed under Rule 2.05.6(3)(b)(iii), Surface Water Probable Hydrologic <br />Consequences. After mining operations at the Foidel Creek Mine have been completed and the mine workings <br />are allowed to flood, there is the potential for water quality effects on units that are in communication with the <br />workings. The increased surface area of rock material that has been exposed to weathering is more susceptible <br />to leaching by the ground water in the flooded workings. This may lead to increased solute concentrations and <br />changes in water chemistry characteristics. As pre - mining potentiometric levels and ground water flows are re- <br />established, discharge of this lower quality water to other units and to surface streams may occur. The effects of <br />this occurrence are discussed under Rule 2.05.6(3)(b)(iii), Probable Hydrologic Consequences Ground Water <br />System Effects on Ground Water Quality of Aquifers. <br />Leaching of waste rock material in disposal areas upgradient from the underground mining operation, and of <br />caved and fractured material in and above the mined workings is unavoidable and will result in increased TDS <br />levels in affected Wadge and Wolf Creek overburden ground water units. Once leaching has occurred, there is <br />no practical technology currently available to treat the water to decrease TDS concentrations. Progressive <br />decreases in TDS levels will occur after sufficient water has percolated through the newly exposed material; <br />however, this may take several hundred years under existing hydrologic conditions, The only method to <br />minimize the impacts of mine - related leaching on ground water quality is to minimize the amount of water <br />which can pass through these materials. The effects of leaching are discussed in Effects on Ground Water <br />Quality of Aquifers and Surface Water Systems - Impacts of Mine Discharge, below. <br />Note that, despite some unavoidable increase in TDS concentrations or change in ion balance, the overall ground <br />water impacts arc limited to this relatively insignificant overburden unit. Water supply wells in the overburden <br />TR13 -83 2.05 -133 11/03/14 <br />